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As the Moon traces its orbit around the Earth, we see different proportions illuminated by the Sun. Once in each orbit, our satellite is totally illuminated - a full moon.

And as the Moon orbits the Earth every 27 days or so, it travels in an elliptical or oval shape.

This means that its distance from our planet is not constant but varies across a full orbit.

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Media captionNewsround: What is a supermoon?

But within this uneven orbit there are further variations caused by the Earth's movements around the Sun.

These mean that the perigee - the closest approach - and full moon are not always in sync.

But occasions when the perigee and full moon coincide have become known in popular parlance as supermoons.

Taking good photos of the "supermoon"

Prof Tim O'Brien from the University of Manchester advises skywatchers to look to the east, where the Moon rises, for the best view. Go somewhere with a low horizon, away from obstructions like tall buildings.

He says there is an optical illusion when the Moon is low on the horizon that makes it look bigger.

For the perfect snap, Nasa photographer Bill Ingalls suggests using a reference point: "Don't make the mistake of photographing the Moon by itself with no reference to anything," he says.

He also advises scouting locations a day or two in advance and, if you are using a digital SLR, using a daylight white balance setting to capture moonlight.

To observers, the differences between a supermoon and a normal full moon are quite subtle.

Generally, supermoons can be up to 14% larger and 30% brighter, but only when compared with the furthest point the Moon gets to within its orbit.

"These differences are pretty small, and with the Moon rising so high in the sky, as it does in the winter months, it'll be quite hard to notice any difference without comparing photographs," Dr Chris North told The Conversation website.

"But regardless of how big and bright it looks, the Moon really is a beautiful object to look at."

However Neil de Grasse Tyson, director of the Hayden Planetarium in New York, has previously suggested the events are just a little bit over-hyped.